REF: De-duplicate MultiIndex._get_indexer (#41976)

Author: jbrockmendel

pandas/core/indexes/base.py

@@ -3497,6 +3497,13 @@ def _get_fill_indexer(
         self, target: Index, method: str_t, limit: int | None = None, tolerance=None
     ) -> np.ndarray:
 
+        if self._is_multi:
+            # TODO: get_indexer_with_fill docstring says values must be _sorted_
+            #  but that doesn't appear to be enforced
+            return self._engine.get_indexer_with_fill(
+                target=target._values, values=self._values, method=method, limit=limit
+            )
+
         target_values = target._get_engine_target()
 
         if self.is_monotonic_increasing and target.is_monotonic_increasing:

pandas/core/indexes/multi.py

@@ -2672,18 +2672,9 @@ def _get_indexer(
                 # TODO: explicitly raise here?  we only have one test that
                 #  gets here, and it is checking that we raise with method="nearest"
 
-        if method == "pad" or method == "backfill":
-            # TODO: get_indexer_with_fill docstring says values must be _sorted_
-            #  but that doesn't appear to be enforced
-            indexer = self._engine.get_indexer_with_fill(
-                target=target._values, values=self._values, method=method, limit=limit
-            )
-        else:
-            indexer = self._engine.get_indexer(target._values)
-
         # Note: we only get here (in extant tests at least) with
         #  target.nlevels == self.nlevels
-        return ensure_platform_int(indexer)
+        return super()._get_indexer(target, method, limit, tolerance)
 
     def get_slice_bound(
         self, label: Hashable | Sequence[Hashable], side: str, kind: str | None = None